Huge underground pyramids in Bosnia?

Cynical me thinks they're just hills, but serious investigations have begun to determine if three pointy hills in Bosnia are actually buried pyramids. Hmm. How would they cover them with so much dirt as to resist erosion for all these years?

More at the BBC, or just by googling the subject for sites of drooling fans.

Even if all the archaeologists find are a series of multi-thousand-year-old tunnels, that's pretty interesting. I've always been interested in ancient feats of human engineering, particularly less-famous ones such as Serpent Mound (below), which is located near me. And of course the real Pyramids, Machu Picchu, etc.